With advancements in molecular biology, genes associated with lipid/lipoprotein disorders [in particular, atherosclerotic cardiovascular disease, (CVD)] have been recently identified and characterized. We studied the gene for apolipoprotein(a) and its product, apolipoprotein (a), for improved diagnosis of patients and for better understanding of pathogenic events involved in the development of cardiovascular disease. Comprehensive studies allowed the identification of serum apo(a) isoforms in terms of structure (i.e., the number of repeat "kringle" units), as opposed to earlier arbitrary isoform assignments with no universally understandable nomenclature and numerous inaccuracies Despite a generally inverse correlation between apo(a) isoform size and serum apo(a) concentration, we found evidence that isoform size is not the only factor that determines serum apo(a) levels. individuals who lack any detectable serum apo(a) concentration (the so-called "null" phenotype) were found to carry two alleles of the apo(a) gene. Thus, structural changes in the gene or in its regulatory unit(s) that prevent expression of the gene may be responsible for the "null" phenotype. Two alleles of the apo(a) gene and free (!) apo(a) protein were detected in the serum of a patient with abetalipoproteinemia. Further studies are necessary to better understanding of the apo(a) gene and its intriguing product, apo(a), the unique component of the Lp(a) particle.